Among the more common conditions shared by humans generally is the presence of lesions on the skin, many of which are pigmented in one or more colors and some of which are considered abnormal although not always dangerous to the individual. Typical examples of naturally occurring pigmented lesions include freckles; age or liver spots; birth marks; malignant melanomas; nevi (melanocytic, epidermal, vascular, and connective tissue); and lentigines (brown spots on the skin or mucous membrane). In addition, a person's skin may have abnormalities due to vascular lesions which are caused by an abundance of enlarged blood vessels. Common examples of vascular lesions are "port wine" stain birth marks; telangiectasis, a spot formed most commonly on the skin by a dilated capillary or other small blood vessel; and hemangioma, a benign tumor composed of well-formed blood vessels and classified as capillary or cavernous.
In comparison, intervention created pigmented lesions are commonly called "tattoos" and are commonly divided into two different categories: human-caused tattoos and traumatic-inflicted tattoos. Traumatic-inflicted tatoos are created typically as a result of accidents or other mishaps which cause scrapes, abrasions, or lacerations in a manner such that foreign material inadvertently becomes embedded into the skin. During the healing process, the skin becomes pigmented and often scarred as a result. In comparison, human-created tattoos are a popular form of skin decoration and self-expression in many cultures and societies. A common example here in the U.S. is the tattooed sailor; and it has been estimated that as many as 10% of the U.S. general population have tattoos somewhere on the skin of their bodies.
Tattoos are usually pigmented creations and the work of both professional and/or amateur artists who deposit special dyes and/or inks into the skin to create distinctive coloration and patterns which then remain visible over the life of the individual. Tattoos can range in size from a few millimeters in diameter to patterns covering the entire body. In addition, tattoos can also be created using either single or multiple colors. Multiple colored tattoos tend to be done by professional tattooists because of their difficulty and via the use of different colored dyes and inks. The colors employed in a single tattoo can include black, blue, red, yellow, orange, green, purple, and white; the most common colors being black and blue because they are often used to outline the borders of the tattoos themselves. It has also been reported that although many different colors are tattooed into the skin, certain colors tend to fade after one or two years; these are red, yellow, and orange. Thus, the colors which are most commonly found in tattoos of advancing age are usually black, blue, and green. Moreover, the professional tattooist usually creates the tattoo pattern using a vibrating needle which limits the depth into which the pigment(s) is introduced into the skin--usually to the papillary layer of the dermis. In addition, the pigments used by the professional tattoo artists typically include India ink and, increasingly, metallic compounds which have replaced organic materials as the means to produce vivid colors other than blue-black [Slater et al., Clin. Exp. Dermatol. 9:167-173 (1984)].
Non-professional tattoos, by contrast, tend to be of a single color, most commonly black or blue. The pigment employed by the amateur tattooist usually is carbon particles (from India ink, soot, or charcoal); and the blue-black appearance of the amateur tattoo is caused by increased scattering at shorter light wavelengths in the dermis because the color of the pigment particles is actually black. In the more crudely created amateur tattoo, the pigment is introduced generally throughout the dermis in an uncontrolled manner because of the hand-held needle traditionally employed for this purpose. Other major differences between the professionally created tattoo and the amateur tattoo include the depth to which the pigment is tattooed into the skin (because professional tattoos tend to be at an even depth lying mainly in the mid-dermis whereas non-professional tattoos tend to vary from site to site); and the density of particles at the tattoo site (professional tattoos typically are dense and evenly distributed whereas amateur created tattoos vary in density from site to site).
It will be recognized and appreciated that many persons at some point in their lives wish to remove pigmented lesions, whether normal or abnormal, from their skin for health and/or cosmetic reasons. Even those individuals who voluntarily choose to create a tattoo on their skin may subsequently choose to undergo treatment designed to remove the tattoo--often because of advancing age, or via a change in lifestyle, or through a new personal relationship. Presently existing modes of treatment may achieve some clearing or lightening of pigmented skin areas but only at substantial risk for the individual because of severe changes to the pigmentation on the skin or the creation of actual scarring of the treated skin area. The risks and severity of the varying problems associated with removing pigmentations and other lesions generally of the skin is best evidenced and demonstrated by the difficulties of removing tattoos.
It is valuable to understand the mechanism of tattoo formation in order to better comprehend the deficiencies and risks presented by conventionally known methods for removing tattoos. An electron microscopic study of amateur created and professionally created tattoos to ascertain the mechanism of tattoo formation has been recently published [Lee P.J. and A. Pawlowski, Int. J. Vermatol. 26:453-458 (1987)]. It was found that an acute inflammatory reaction immediately followed the tattooing process; and the various pigment particles deposited in the skin migrated to the dermis through a destroyed basement membrane. Then, as the skin subsequently healed, the basement membrane reformed and the amount of pigment within epidermal cells decreased. The pigment particles, however, were found to be aggregated within dermal fibroblasts in established tattoos. Correlative with this information is the conventional knowledge regarding the absorption spectrum of melanin and the absorption spectrum of charcoal, the two most commonly used materials in tattoos [Wolbarsht et al., Appl. Optics. 20:2184-2186 (1981)]. The spectrum of charcoal is representative of both amateur created and blue-black professionally created tattoo pigments (carbon particles from either India ink and/or soot). The relative optical density of melanin has a nearly exponential form in the ultraviolet and visible regions of the spectrum and drops off rapidly with increasing wavelengths. In comparison, the optical density of charcoal remains essentially constant throughout the visible region.
Since the tattoo pigment is inside the skin (i.e., the dermis) destructive modes of treatment to remove this pigment have had to be employed. As is evident, a major problem has been access to the dermal pigment; therefore, the only way it has been possible to remove the pigment(s) without using laser apparatus has been to remove all the skin around the tattoo from the most exterior surface downwards into the deep tissues.
The conventional modes of treatment used for tattoo removal thus presently include: surgical excision and skin graft; dermabrasion; saliabrasion; cryosurgery; and laser light generated by CO.sub.2, argon, Nd:YAG, and ruby lasers [Hirshowitz, D.E., Plast. Reconstr. Surg. 373-378 (1980); Scutt, R. W. B., Br. J. Hosp. Med. J. 8:195 (1972); Manchester, G.H., Cutis 7:295 (1971); Clabaugh, F.M., Plast. Reconstr. Surg. 55:401 (1975); McDowell, F., Plast. Reconstr. Surg. 53:580 (1974); and Groot et al., J. Am. Acad. Dermatol. 15:518-522 (1986).
Even the conventional laser treatment methods have generally caused damage to both pigmented and non-pigmented cells in the skin; and the laser treatment of the skin lesions has varied markedly from merely superficial to extremely deep with little attempts to control the amount of tissue destroyed. Moreover, the laser treatment processes known to date cause a change in skin texture. The skin is altered from being smooth, elastic, and mobile to being hard, immobile becoming bumpy, cratered, or pitted. In addition, there is loss of the normal skin markings (normal ridges and valleys) as well as changes in normal skin pigmentation (loss as well as increase in normal skin color). Therefore, the change in skin texture is almost always also accompanied by a change in skin color where the skin of the treated site is no longer normal in color. Instead, the treated skin appears either porcelina-white or mottled with dark pigment, both of these resulting from either loss of all pigment or the implanting of pigment in the dermis instead of the epidermis. All of these changes result from extensive, severe damage induced by the different laser treatment modalities.
Even the ruby laser (the best of the conventionally used laser systems) has been demonstrated to be flawed, deficient, and inefficient for removing pigmentations, lesions, and abnormalities from the skin of a living human. There are many problems concomittant with or caused by the ruby laser system and its various modes of use. In one mode, the ruby laser emits its laser light pulses in short bursts of pulses often called a normal mode pulse train. A pulse train becomes problematic when the pulses are of low power. When this occurs, and provided the pulses are discharged frequently enough, the effect on the tissue will be similar to that of a continuous wave laser. Moreover, instead of destroying the targeted structure with each pulse, because the ruby energy output is low, there is only sufficient energy to partially alter the target. If the pulses are discharged frequently enough then this effect on the target will be cumulative producing an effect which is similar to the continuous wave (cw) laser. Also, due to the characteristics of the ruby laser itself, the intensity of each pulse burst can vary and it is very difficult to control the light energy dose delivered to each treatment site.
In addition, there presently is no convenient or easy way of delivering the laser light beam to the patient. The only way of performing this manipulation at present is by the use of an articulating arm which is not only cumbersome but also easily goes out of alignment. This results in a further decrease of laser energy available to destroy the targeted tissue, thus making the ruby laser system even less efficient for removing abnormal pigmentations. In addition, the ruby laser has been shown to produce severe scarring even when employed in the normal mode.
A second way to operate the ruby laser system is in the Q-switched mode. In this alternative mode of use, a single energy pulse of short duration is delivered by the ruby laser. However, despite the use of Q-switched ruby lasers in clinical studies since the 1960's, the only currently available means of delivering treatment energy pulses is by means of an articulated arm which is not only difficult to align and is bulky, but also creates "hot spots" within the delivered light beam. One reported study revealed that multiple treatments using the ruby laser in the Q-switched mode were required to remove at least 90% of the pigment in the skin. Adverse effects of hyper- and hypo-pigmentation were noted in some patients; and tattooed sites composed of colors other than blue-black were not affected directly but showed a whitening of the skin subsequent to treatment [Read et al., Br. J Plast. Surg. 36:455-459 (1983)]. Another study [Taylor et al., Arch. Dermatol. 126:893-899 (1990)] reported substantial lightening or total clearing of skin was found in 78% of amateur tattoos and 23% of 13 professional tattoos; but that multiple retreatments were required, transient hypopigmentation was seen in 50% of treated tattoos, and scarring appeared in approximately 6% of patients.
As a consequence, there is major interest in developing alternative laser apparatus and laser delivery systems which could be modified for use in an improved and carefully controlled method for removing pigmentation, lesions, and abnormalities from the skin of a living human. It will be recognized and appreciated that while the development of new laser equipment and new laser delivery systems constitutes one discrete area of technical research, such efforts are meaningfully different and distinct from investigations involving humans directed to developing a clinical process and methodology under carefully controlled operational parameters which would be effective and useable by a dermatologist or other medical practitioner. Equally important, the development of a clinically effective therapeutic treatment using a carefully controlled laser apparatus and laser delivery system which would prevent hypo- and/or hyperpigmentation as well as cratering/pitting and elevation or destruction of dermal and/or epidermal layers of the skin would be generally recognized as a major improvement and advance by practicing dermatologists and clinicians treating patients on a regular basis.